In ordinary life, we can control whether the light in our living rooms is on or off by reaching for the light switch. When the space for light is reduced to a few nanometers, quantum mechanical phenomena take over, and it is uncertain whether there is light or not. Both may occur simultaneously, as scientists from the Julius-Maximilians-Universität Würzburg (JMU) and the University of Bielefeld demonstrate in the journal Nature Physics.
“Detecting these novel states of quantum physics on the tiny scales of electrical transistors might aid in the development of optical quantum technologies for future computer chips,” says Bert Hecht, a professor at Würzburg. His group created the nanostructures under investigation.
Our digital world’s technology is built on the idea that either a current flows or it does not: one or zero, on or off. There are two distinct states. In quantum physics, however, it is feasible to ignore this concept and build an arbitrary superposition of the seeming opposites. This multiplies the possibilities for transferring and processing data several times over. Such superposition states have been known for a long time, particularly for light particles known as photons, and are exploited in the detection of gravitational waves.
Quantum states have been discovered.
A group of physicists and physical chemists from Bielefeld and Würzburg has now succeeded in directly detecting such light superposition states in a nanostructure. Light is caught in a nanostructure and coupled to electronic oscillations, which are known as plasmons. This permits light energy to be maintained in situ on the nanoscale.
The researchers studied how many photons from a light pulse couple to the nanostructure in the experiment led by Würzburg professor Tobias Brixner. As a consequence, there is no photon and three photons at the same time. Brixner elaborates, “This signature was quite difficult to detect. Photons can be detected extremely effectively with sensitive detectors; but, adequate techniques did not exist in the nanoworld for single photons, which are also in a quantum mechanical superposition state.” Furthermore, photons and electrons are connected for less than a millionth of a millionth of a second before decaying, giving little time for detection.
Highest combined spatial and temporal resolution
A unique detector was utilised in the tests that have recently been published. “The energy produced during the decay of the state is sufficient to liberate additional electrons from the nanostructure,” adds Bielefeld Professor Walter Pfeiffer, who was instrumental in building the physical model and evaluating the results. Using a photoemission electron microscope with a resolution of a few nanometers, the activated electrons may then be recorded in an image. Because of the short decay durations, ultrashort laser pulse sequences were employed to extract the “fingerprint” of the light’s superposition states.
This is the first step towards the ultimate objective of directly studying the complete quantum physical state of linked photons and electrons at the nanoscale. A procedure characterised by the word tomography, as in medicine. Thus, the lights in the scientists’ offices and labs should always be turned on.
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